Wait for the server configuration before starting features

As the server configuration endpoint can be used to enabled/disable features and tweak parameters impacting all users, it was the natural move to first wait for it before starting features. Here is the flow when starting the application: 1. Launch engines (an engine is an account). 2. Fetch the server configuration endpoint. 3. Update options, merge with one from the local configuration file. 4. Start (or deny) all features.